The marketing of cut flowers and ornamental flowering plants is of considerable economic importance to the horticultural industry. In 1989, for example, the wholesale United States market for cut flowers and flowering, foliage, and bedding plants amounted to approximately 2.43 billion dollars. The sale of cut flowers contributed approximately 459 million dollars to this total, with the sale of potted flowering plants contributing approximately 522 million dollars.
Cut flowers are subjected to considerable stress during harvesting, handling and shipping, and their vase life, once in the hands of the ultimate consumer, can be considerably shortened as a result. It has been known for some time that plants produce ethylene, particularly in response to stress, by converting methionine into 1-aminocyclopropane-1-carboxylic acid (also known by the acronym "ACC") which is then further converted into ethylene. The plant enzyme responsible for the production of ACC is ACC synthase. Ethylene, a gaseous phytohormone, is believed to be involved in the modulation of a number of plant biochemical pathways affecting such processes as abscission, senescence, flowering, fruit setting, fruit ripening, seed germination, sex expression, root growth, internode elongation, epinasty, and geotropism.
Based upon this understanding of the mechanism of wilting or senescence in cut flowers, various formulations have been suggested in the prior art for preserving the vase life of cut flowers by incorporating agents known to block the activity of ACC synthase. Among cut flower preservative agents which have been suggested in the prior art are L-trans-2-amino-4-(2-aminoethoxy)-3-butenoic acid (also known by the common name "aminoethoxyvinyl glycine" and the acronym "AVG"), and carboxymethoxylamine (also known by the common name "aminooxyacetic acid" and the acronym "AOAA"). J. E. Baker, et al., Hort. Science, 12(1): 38-39 (1977) have reported, for example, that immersing the stems of cut carnations (Dianthus caryophyllus, L.) in solutions containing AVG, either alone or in combination with free-radical scavengers such as sodium benzoate or propyl gallate, extended the vase life of the cut flowers. Similar effects on extension of the vase life of cut flowers following treatment with solutions containing AVG have been shown for snapdragons (R. E. Hardenburg, et al., J. Am. Hort. Soc., 102: 517-520 (1977)) and for irises, daffodils, and chrysanthemums (C. Y. Wang, et al., Hort. Science, 14: 59-60 (1979)). Canadian patent 1,240,173 to Gladon teaches a method of preserving cut flowers by immersing the stems in a solution containing AOAA.
Cut flower preservative formulations taught in the prior art include a sugar which provides an energy source for the cut flowers, an antimicrobial agent (believed to prevent clogging by microbial growth of the vascular system of the cut flowers), and inorganic salts. A review of the common ingredients of cut flowers preservative formulations is provided by A. H. Halevy, et al., Horticultural Reviews, 3: 59-143 (1981).
While the method of preserving cut flowers by immersing cut flower stems in solutions containing an ACC synthase inhibitor such as AVG or AOAA is generally known, the prior art has not addressed the problem of how to prepare dry, solid formulations which contain these agents and which have the requisite stability to permit their preparation and storage for extended periods prior to use. Solid formulations containing AVG or AOAA together with an acidic inorganic salt and a sugar, intended for later use in preparing cut flower preservative solutions, tend to lose their effectiveness over time. There is thus a need for solid cut flower preservative formulations containing AVG or AOAA which have the requisite stability to permit pre-packaging and storage for extended periods prior to their use.